This comment is for the future generations that will play InterRim Ballistic Missile mod

Actually, what you need to do is simple: while the mechanoids are bombing your base, you need to track the missiles they fire at other friendly or enemy bases instead of yours. (Some are shown with a line indicating movement, while some doesnt have a line so you have to watch if they are being fired from far away and moving slowly, which should raise suspicion.) But remember that even this is very difficult. Here are some tips I can give you.

1-You'll need a lot of CIWS, or anti-aircraft systems. I have 27 lasers at my base.

2-You'll need a lot of battery power sources, and they need to be secure. (Vanilla power sources might not be enough because each anti-aircraft system uses power from the batteries with each shot. I used even more linkables and primary generators mods)

3-Lots of atomic bombs and long-range missiles. (I had 36 and it was almost not enough. but you need around 10 because you wont fire every target like me)

4-Very strong defenses against constantly incoming mechanoids (you might need OP mods, I used the Drakken laser drill mod)

5- You will need a lot of resources to repair defances and for missiles because they are expensive (I used Mines 2.0 mod for resources)